Zirconium and hafnium-catalyzed polymerization of methylenecyclopropane

ABSTRACT

A polymer having a repeating unit of   &lt;IMAGE&gt;   and a method for preparing it through Zr-catalyzed polymerization of methylenecyclopropane is disclosed.

The United States Government has rights in this invention pursuant toDOE Grant No. DE-FG02-86ER13511.

This is a division of application Ser. No. 08/399,390, filed Mar. 6,1995, U.S. Pat. No. 5,480,952, which is a continuation-in-part of patentapplication, Ser. No. 136,217, filed Oct. 14, 1993, U.S. Pat. No.5,395,906, which is a continuation-in-part of Ser. No. 962,390, filedOct. 16, 1992, now U.S. Pat. No. 5,300,598.

BACKGROUND OF THE INVENTION

This application relates to catalysts and more particularly tohomogeneous catalysts for use in polymerization via the ring opening ofstrained ring systems, and the polymers formed with such catalysts.

As discussed in U.S. Pat. No. 5,300,598, in the presence of ring-openingZiegler catalysts, methylenecyclobutane can be polymerized into apolymer consisting of the structure A, through a ring-opening mechanism.##STR2##

Polymers having rigid backbones often possess unique propertiesincluding high modulus and strength, chirality, and liquid crystallinitywhich properties lend themselves to use as a structural components orthermoplastic elastomers in structural applications such as fibers,aircraft and automotive parts or in optical devices, such as liquidcrystal displays and others. Examples are polyisocyanides,polycarbodiimides, polybenzimidazoles, polyacetylenes, polyimides, andpolyamides. The structural stiffness of these polymers is frequentlyachieved through delocalized π bonding and secondary chemicalinteractions such as hydrogen bonding. Linear rigid macromoleculesconsisting solely of saturated hydrocarbon backbones, the rigidity ofwhich derives from σ bond linkages, are virtually unknown, and wouldrepresent a new class of isomeric polyolefins. One apparent reason forthe paucity lies in the lack of efficient synthetic approaches, sincetheir logical monomeric precursors would necessarily be olefins, whichhave limited polymerization pathways. However, electrophilic d^(o)metallocene centers appear to be highly efficient in a number ofcarbon-carbon bond transformations.

SUMMARY OF THE INVENTION

Therefore, an object of the subject invention is a novel catalyst toproduce polymers having a rigid backbone.

A further object of the subject invention is a polymer formed from acatalytic olefin polymerization process which operates via aring-opening mechanism.

A still further object of the subject invention is a polymer formedthrough the use of a catalyst by which electrophilic metallocene cationscatalyze the facile regioselective ring-opening homopolymerization ofmethylenecyclopropane type monomers using well-defined homogeneous Zr,Ti, and Hf catalysts.

A further object of the subject invention is a polymer of the structure:##STR3## which may be depicted as: ##STR4##

These and other objects of the subject inventions attained by a methodinvolving the sequential ring-opening-zipping-up Ziegler polymerizationof methylenecyclopropane catalyzed by (Me₅ Cp)₂ MMe⁺ MeB(C₆ F₅)⁻, (M=Ti,Zr, Hf) and the characterization of the resulting rigid-rod/helixpolymer of structure B, including the structure A above.

In the alternate nomenclature of the American Chemical Society, andfocusing on the smallest structural repeating unit, the polymer of thesubject invention can be named poly(1,4:2,2-butanatetrayl), and thus isrepresented by the structure ##STR5## Polymerization ofmethylenecyclopropane proceeds rapidly in a dilute toluene solutions of(Me₅ Cp)₂ MMe⁺ MeB(C₆ F₅)⁻, (M=Zr, Hf) under rigorouslyanhydrous/anaerobic conditions even at temperatures as low as -30° C. toresult in the polymer poly(1,4:2,2-butanatetrayl) having a typicalmolecular weight of 1,000-39,000. The resulting polymers are isolatedafter toluene removal followed by washing.

BRIEF DESCRIPTION OF THE DRAWINGS

The Figure is a schematic of the reaction sequence for preparing thepolymers of the subject invention.

DETAILED DESCRIPTION OF THE INVENTION

Facile β-alkyl transpositions are a distinctive feature of electrophilicd^(o) f^(n) hydrocarbyl chemistry (e.g., equation (I)) and ##STR6##represent an important chain transfer channel in certain olefinpolymerization processes. In principle, such transpositions might alsoprovide an unusual pathway to functionalized polyolefins by couplingolefin insertion and strained monomer ring-opening sequences (equationII)). ##STR7## In the presence of conventional heterogeneousZiegler-Natta catalysts, methylenecyclopropane undergoes a sluggishreaction to afford polymers having ring-opening or mixedring-opening/insertion-derived microstructures. The ring-openedstructures were ascribed to oxidative addition at the C3-C4 junctures ofA. As stated above, the subject invention involves electrophiliczirconocene or hafnocene cations, which catalyze the facile,regioselective ring-opening homopolymerization of exo-methylene cyclicorganic compounds via a β-alkyl shift mechanism.

The exo-methylene cyclic organic compounds which may be used in thesubject invention generally may be represented by the formula: ##STR8##where R', R", and R"' are organic fragments which may include O, N, S orP. Preferably, the monomer is methylenecyclopropane.

In general, reaction of the catalyst L₁ L₂ MR⁺ X- or (LR'₂ SiNR")MR⁺ X⁻,where L is a cyclopentadienyl-containing ligand, M=Zr or Hf, and. R, R"is an alkyl (C=1-5), hydride, or aryl (C=5-20), X⁻ is a non-coordinatingcharge-compensating anion derived from B(C₆ F₅)₃, B(C₆ F₅)₄, ormethylalumoxane or (L₂ LnH)₂ (Ln=a lanthanide element) withmethylenecyclopropane or a substituted methylenecyclopropane proceedsrapidly in toluene solution to yield, after work-up, a polymer with astructure such as B. Examples of viable catalysts are (C₅ Me₅)₂ ZrMe⁺MeB(C₆ F₅)₃ - and [(C₅ Me₄ (SiMe₂)NtBu] ZrMe⁺ MeB(C₆ F₅)₃ - , or (C₅H₅)₂ ZrR₂ and methylalumoxane, (R=alkyl, aryl, hydride, halide oralkoxide C=1-102). Other nonpolar solvents, both aliphatic (C=1-12) andaromatic (C=6-20) as well as others may be used. ¹ H and ¹³ C NMRspectra reveal that the polymer microstructure which results isdependent on the ancillary ligands at the metal center with L¹ =L² =η⁵-Me₅ C₅ and L¹, L² =Me₄ C₅ (SiMe₂)N^(t) Bu giving highest selectivity.The length of reaction time/extent of conversion appears to have nodetectable effect on selectivity.

EXAMPLES

All operations were performed with rigorous exclusion of oxygen andmoisture in flamed Schlenk-type glassware in a dual manifold Schlenkline or interfaced to a high vacuum (10⁻⁵ torr) system, or in a nitrogenor argon filled glovebox with a high capacity atmosphere recirculator.Argon, ethylene and propylene were purified by passage through asupported MnO oxygen removal column and a molecular sieve column.Aliphatic hydrocarbon solvents were pretreated with concentrated H₂ SO₄,KMnO₄ solution, MgSO₄ and Na, 4 Å molecular sieves. All reactionsolvents were distilled from Na/K/benzophenone under nitrogen and werecondensed and stored in vacuo in bulbs on the vacuum line containing asmall amount of [Ti(η⁵ -C₅ H₅)₂ Cl]₂ ZnCl₂ as indicator.Methylenecyclopropane was additionally dried over Na/K.

EXAMPLES

Preparation of Catalyst

Synthesis of (C₅ Me₅)₂ ZrMe+MeB(C₆ F₅)₃ -

(C₅ Me₅)₂ ZrMe₂ (0.148 g, 0.379 mmol) and B(C₆ F₅)₃ (0.194 g, 0.379mmol) are loaded into a 25 mL flask. Benzene (10 mL) was then vacuumtransferred into this flask at -78° C. As the mixture is slowly warmedto ambient temperature. A clear solution is first seen but it quicklybecomes cloudy as solids begin to precipitate. After stirring for 2.5 h,the mixture is filtered. The light yellow solid is washed once with asmall amount of benzene and dried under vacuum. Yield, 65%.

Synthesis of [C₅ Me₄ (SiMe₂) N^(t) Bu]ZrCH₃ ^(+CH) ₃ B (C₆ F₅)₃ -

C₅ Me₄ (SiMe₂)N^(t) Bu (0.148 g, 0.400 mmol) and B(C₆ F₅)₃ (0.205 g,0.400 mol) are loaded into a 25 mL flask in the glovebox. Benzene (15mL) is then vacuum-transferred into this flask at -78° C. The mixture isslowly warmed to room temperature and stirred for 1.5 h. At this time,large quantities of solid precipitate. Pentane (10 mL) isvacuum-transferred into the flask and the mixture is filtered afterstirring. The light yellow solid is washed once with 5 mL of pentane anddried under vacuum. Yield, 72%.

EXAMPLE 1

Homo-polymerization of Methylenecyglopropane.

(C₅ Me₅)₂ ZrMe⁺ MeB (C₆ F₅)₃ - (6 mg) is loaded into a 25 mL flask in aglovebox. Toluene (10 mL) and methylenecyclopropane (0.1 mL) arevacuum-transferred into the above flask at -78° C. The flask isbackfilled with Ar and the solution stirred at room temperature for 16h. After removing the volatiles under vacuum, the polymeric product iswashed several times with toluene and dried under vacuum. Yield, about90%. The polymer is characterized by ¹ H, and ¹³ C NMR spectroscopy. ¹H(tol-d₈ RT) δ 1.6 ppm; ¹³ C(tol-d₈, 105° C.) δ 41.32(t, ¹ J_(C-H)=126.3 Hz) ppm, 50.11(s), 56.66(t, ¹ J_(C-H) =128.2 Hz).

EXAMPLE 2

Polymerization of Methylenecyglopropane by [C₅ Me₄ (SiMe₂) N^(t) Bu]ZrMe⁺ MeB (C₆ F₅)₃ -.

C₅ Me₄ (SiMe₂) N^(t) BuZrMe⁺ MeB (C₆ F₅)₃ - (19.5 mg) is loaded into a25 ml flask in a glovebox. Toluene (10 ml) and methylenecyclopropane(1.0 ml) are vacuum-transferred into the flask at -78° C. The solutionis stirred at room temperature for 1 hour. The solution turns into asolid phase. The white solid polymeric product is collected by washingwith ethanol and dried under vacuum.

The resulting polymers have been characterized by a combination ofseveral NMR techniques at high temperature. Both ¹ H and ¹³ C spectraindicate that the polymer chains have saturated hydrocarbon backbones.DEPT ¹³ C experiments show that the three major resonances at δ 55, 51and 42 ppm are secondary, quaternary, and secondary carbon atoms,respectively. The intensity of these three signals has a ratio of 1:2:2.Two-dimensional HETCOR experiments reveal that the major components ofthe proton spectrum (δ 1.5-1.7 ppm) are attached to the carbons at δ 55or 42 ppm. The pattern of the linkage between the carbon atoms is thendetermined to be C_(55ppm) -C_(51ppm) -C_(42ppm) by two-dimensional ¹³ CNMR. The only chain structure compatible with the above observations isstructure B. The structure of the chain is also supported by formationof the same polymer in the reaction of polymer A in concentrated toluenesolutions of (Me₅ Cp)₂ ZrMe⁺ MeB (C₆ F₅)⁻⁵ at room temperature. Theunopened cyclopropyl structures (a signal at δ 0.5 ppm in ¹ H spectrumand those at δ 14 ppm in ¹³ C spectrum) observed are assigned to endgroups of the polymer based on the absence of significant quantities ofthe unzipped precursor structure A. The terminal olefinic structure(signals at δ 5.1 ppm, and 2.2 ppm of the allylic proton) can beassigned to either structure A or end groups which are the result ofβ-methyl elimination, apparently polymers produced at lowertemperatures.

The formation of polymeric structure B can be rationalized by aring-opening-zipping-up mechanism (The Figure). The reaction must beginwith the ring-opening polymerization of methylenecyclopropane. Then at acertain step, competing intramolecular C═C bond insertion is initiated,and the zipping-up process starts. That the isomerization of A to Brequires high catalyst concentrations and prolonged reaction time arguesagainst the extensive participation of intermolecular mechanisms whichinvolve first the elimination of the polymer A from the catalyticcenter, and then reinsertion of vinylic end groups of the polymer Afollowed by sequential zipping-up reactions. Although the initiation ofthe zipping-up process can follow several possible routes, observationof the cyclopropyl structures as end groups suggests that the zipping-upreactions start mainly at the point when one molecule ofmethylenecyclopropane inserts, then instead of β-alkyl shiftring-opening, competing intramolecular insertion of a C═C bond occursleading to sequential intramolecular insertion along the entire polymerchain.

                                      TABLE I                                     __________________________________________________________________________    Polymerization of Methylenecyclopropane Using                                 (Me.sub.5 Cp).sub.2 ZrMe.sup.+ MeB(C.sub.6 F.sub.5).sub.3 -- as               Catalyst.                                                                         Catalyst                                                                           Methylene-                                                                           Reaction    Yield of                                          Entry                                                                             Amount                                                                             cyclopropane                                                                         Temperature                                                                          Reaction                                                                           Polymer                                                                            M.sub.w (M.sub.n).sup.d                      1000)                                                                             (mg) (mg)   (°C.)                                                                         Time (h)                                                                           (mg) (x                                           __________________________________________________________________________    1.sup.a                                                                           6.5  398    -30    2.5  340  7,100(1,200)                                 2.sup.b                                                                           5.0  70     0      4.0  50   29,700(11,300)                               3.sup.a,c                                                                         10.2 230    25          160  39,200(13,900)                               __________________________________________________________________________     .sup.a Toluene (15 mL) as solvent                                             .sup.b Reaction in NMR tube, toluene -d.sup.8 as solvent                      .sup.c Dihydrogen was used to reinitiate the reaction at 20 min intervals     The total reaction time was 4 hours.                                          .sup.d GPC vs polystyrene                                                

The regioselectivity of polymerization decreases at high temperature,and the composition having structure A increases. Fractions soluble in amixture of toluene/ethanol (2:1 in volume) are enriched in structure A.Interestingly, polymerization pauses at room temperature beforemethylenecyclopropane is completely consumed. The loss of activity isnot due to poisoning of the catalyst since dihydrogen can re-activatethe polymerization. Thus, chain length is completely controllable fromas little as n-10 to n=100,000 or more, dependent on the supply ofmethylenecyclopropane.

Since the ¹³ C NMR spectrum only shows three major resonances it wouldappear that the polymerization is stereoselective, in other words thepolymer is either a rod-like polymer as in FIG. 1 or a helix-likepolymer as in FIG. II. The control over stereochemistry during zippingup must be related to the relative conformation of the adjacent ringthat formed in the preceding step before since 2 is an achiral compound.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments and equivalents falling within the scope ofthe appended claims.

Various features of the invention are set forth in the following claims.

We claim:
 1. A method for the polymerization of methylenecyclopropanescomprising the steps of adding toluene and methylenecyclopropane orsubstituted methylenecyclopropanes at a temperature of about -78° C. toa flask containing a catalyst of the formula L₁ L₂ MR⁺ RB (C₆ F₅)₃ -(R=alkyl or hydride; M=Ti, Zr, Hf) stirring at 20° C. and recovering thepolymerized product, where L₁ and L₂ are cyclopentadienyl-containingligands.
 2. The method of claim 1 wherein said catalyst is (C₅ H₅)₂ZrMe⁺ MeB (C₆ F₅)₃ -.
 3. A method for the polymerization ofmethylenecyclopropanes comprising the steps of adding toluene andmethylenecyclopropane or substituted methylenecyclopropanes at atemperature of about -78° C. to a flask containing a catalyst of theformula (LR'₂ SiNR")MR⁺ RB(C₆ F₅)₃ - where R=alkyl or hydride; R',R"=alkyl or aryl; M=Ti, Zr, Hf, L=cyclopentadienyl-containing ligand;stirring at 20° C., and recovering the polymerized product.